This invention relates to the use of compositions or admixtures containing a polymer and a phosphonoalkane carboxylic acid in aqueous media for inhibition of scales of alkaline earth metals and anions selected from sulfate, carbonate, bicarbonate, phosphate, fluoride, and hydroxide. In the preferred embodiment, the alkaline earth metals contemplated herein in the context of scale inhibition include calcium, barium, and magnesium. Particular scales contemplated herein include, but are not limited to, calcium carbonate, calcium sulfate, calcium phosphate, calcium fluoride, calcium oxalate, barium sulfate, and magnesium-containing scales.
Most industrial waters contain alkaline earth metal cations, such as calcium, barium, magnesium, etc., and several anions such as bicarbonate, carbonate, sulfate, hydroxide, phosphate, silicate, fluoride, etc. When combinations of these anions and cations are present in concentrations which exceed the solubility of their reaction products, precipitates form until these product solubility concentrations are no longer exceeded.
For example, when the concentrations of calcium ion and carbonate ion exceed the solubility of the calcium carbonate reaction products, a solid phase of calcium carbonate will form.
Solubility product concentrations are exceeded for various reasons, such as partial evaporation of the water phase, change in pH, pressure or temperature, and the introduction of additional ions which form insoluble compounds with the ions already present in the solution.
As these reaction products precipitate on surfaces of the water carrying system, they form scale or deposits. This accumulation prevents effective heat transfer, interferes with fluid flow, facilitates corrosive processes, and harbors bacteria. This scale is an expensive problem in many industrial water systems causing delays and shutdowns for cleaning and removal.
U.S. Pat. No. 4,575,425 is directed to a method for inhibiting precipitation and deposition of calcium oxalate scale in an aqueous system by the use of (a) a compound selected from water-soluble phosphates, phosphonates, and phosphinates, and amino tri(methylene phosphonic acid), and (b) a polyelectrolyte selected from, inter alia, copolymers of acrylic acid and 2-acrylamido-2methylpropane sulfonic acid. A specific example of a phosphonate is 2-phosphonobutane-1,2,4-tricarboxylic acid.
U.S. Pat. No. 4,640,793 discloses an admixture for inhibiting formation of scale forming salts and for inhibiting corrosion of a metal in an aqueous system comprising (a) a polymer of acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid and (b) a compound selected from polycarboxylates, phosphonates, phosphates, polyphosphates, metal salts and sulfonates thereof. A specific example given of a phosphonate is 2-phosphonobutane-1,2,4-tricarboxylic acid.
A companion case for both inventors is being filed on the same date as this case. The companion case is entitled "Stabilization of Metal Ions and Dispersions of Particulates in Aqueous Systems" and covers the use of a copolymer and a phosphorus compound to stabilize metal ions and/or disperse particulates in an aqueous system. The copolymer contains polymerized acrylic acid and the phosphorus containing compound is selected from phosphonates and polyphosphates.